1. Field of the Invention
Polymers used for coating fertilizers are represented by the following general formula: ##STR2## wherein R.sub.1 is hydrogen, alkyl, alkenyl, cycloalkyl, cycloalkyl substituted with an alkyl, alkylene, alkenyl or alkoxy, cycloalkenyl, cycloalkenyl substituted with an alkyl, alkylene, alkenyl or alkoxy, aryl and aryl substituted with alkyl, alkylene, alkenyl and alkoxy; R.sub.2 is an alkylene, alkenylene, cycloalkylene, cycloalkylene substituted with an alkyl, alkylene, alkenyl or alkoxy, cycloalkenylene, cycloalkenylene substituted with alkyl, alkylene, alkenyl or alkoxy, arylene, or arylene substituted with an alkyl, alkylene, alkenyl or alkoxy. The generic formula also embraces in addition to homopolymers, copolymers of the random and block types formed by reacting monomers or mixtures of preformed homopolymers and/or copolymers, branched polymers and cross-linked polymers. In the above formula a is 2 to 3, and n is greater than 10, usually 10 to 100.000.
2. Description of the Prior Art
The reaction of orthoesters with glycols leading to non-polymeric and other diverse products is known to the art in the references such as Ind. J. Appl. Chem., Vol. 28, No. 2, pages 53 to 58, 1965 wherein Mehrota, et al obtained monoethoxy-monoglycolate and triglycoxy-bisorthoformate by reacting orthoformate with hexamethylene glycol in molar ratios of one to one, and two to three to yield low molecular weight compounds. Similarly, Crank, et al in Aust. J. Chem., Vol. 17, pages 1392 to 1394, 1964, disclosed the reaction of triols with orthoesters including ethyl orthoformate with butane-1,2,4-triol, pentane-1,2,5,-triol and pentane-1,3,5,-triol to form monomeric bicyclic compounds. During the preparation of the bicyclic orthoesters by reacting ethyl orthoformate with triols, Crank, et al found that compounds produced from starting materials having a 1,2-diol structure also contained compounds having ethylene linkages. In a subsequent paper, Crank, et al Aust. J. Chem., Vol. 17, pages 1934 to 1938, 1964, developed this reaction into a synthetic procedure for the conversion of 1,2 -diols into olefins. Later, DeWolfe in Carboxylic Ortho Acid Derivatives, 1970, published by Academic Press, Inc., New York, noted that carboxylic orthoesters are more reactive toward acid hydrolysis than almost any other class of compounds, and this high hydrolytic reactivity complicates their synthesis and storage. DeWolfe reported that the conversion of diols to cyclic orthoesters including alkoxydioxolane or alkoxydioxane, followed by acid hydrolysis, provides a method for monoacylating diols. More recently, Bailey reported in Poly. Prepr. Amer. Chem. Soc. Div. Polym. Chem., Vol. 13, No. 1, pages 281 to 286, 1972, that the polymerization of spiro orthoesters at ambient and elevated temperatures led to polyesters and polycarbonates of the structures [--CH.sub.2 CH.sub.2 CH.sub.2 COOCH.sub.2 CH.sub.2 O--].sub.n and [--OCH.sub.2 OCOOCH.sub.2 CH.sub.2 CH.sub.2 --].sub.n. In copending United States Patent Application Ser. No. 544,808 filed Jan. 28, 1975 and now U.S. Pat. No. 4,093,709 issued on June 6, 1978 and assigned to the same assignee of this application, inventors N. Choi and J. Heller disclosed orthoester and orthocarbonate polymers comprising a polymeric backbone having a dioxycarbon unit with a multiplicity of hydrocarbon groups bonded thereto. The polymers of Choi and Heller have both oxygens of the dioxycarbon backbone formed independently of a heterocyclic ring.